Modes

Very often, you want to generate multiple versions of the same document:
one version for printing and one for viewing on the screen, one version for
students and one version for the instructor, and so on. You can do this in a
simple but naive way: create different files set up for the different versions and
\input the common material, or create some new conditional flags using
\newif and set them appropriately for conditional processing. Or you
could use modes—the ConTeXt way of doing conditional processing.

Introduction

A mode is similar to a conditional flag, but with a few advantages: new modes
need not be explicitly defined (no need for something like \newif),
multiple modes can be simultaneously enabled or disabled, and the status of multiple
modes can be checked easily. Moreover, modes can be set from a command line
switch. As a result, multiple versions of a document can be generated without changing
the source file.

The name or identifier of a mode can be any combination of letters, digits, or
spaces. Names starting with * are reserved for system modes.

In this article I explain how to activate a mode and how to check if a mode is
active or not.

Setting modes

The names are self-descriptive. \enablemode activates a mode,
\disablemode deactivates a mode, and \preventmode permanently
deactivates a mode. All three commands take a list of modes as an argument. For
example, you can activate modes named screen and solution with

\enablemode[screen,solution]

Modes can also be activated by a command line switch --modes to
texexec or context. For example, another way to activate the screen and
solution modes, to run ConTeXt using one of:

texexec --mode=screen,solution ...
context --mode=screen,solution ...

Pre-defining modes

Normally, the overhead for testing modes is negligible, but it can add up if modes are tested multiple times in a document (for example, as part of a macro). In such cases, you can define a mode before using them, to speed up the processing. Modes are defined using:

\definemode[...][...]

The first argument is a list of modes; the second argument may be yes, no, or keep. For example,

\definemode[screen][yes] defines a mode and enables it;

\definemode[screen][no] defines a mode and disables it;

\definemode[screen][keep] defines a mode and keeps its previous status.

Typically, it is better to use \definemode[...][keep] so that the modes may be enabled or disabled from command line as well.

Conditional processing based on modes

You may want to process or ignore a chunk of code if a particular mode is enabled
or disabled. Such a chunk of code is specified using \startmode and
\startnotmode environments. Their use is best explained by an example.

Suppose you want to change the paper size of a document depending on whether it
is for print or screen. This can be done in multiple ways. You could set
the default paper size for print and change it in screen mode:

\startmode (and \startnotmode) checks the value of the mode at the time it is executed. This is important when you are setting the modes using \enablemode or \disablemode. For example,

\enablemode[foo]\startmode[foo]
...
\stopmode

the contents of the mode environment are executed because foo is enabled when \startmode is encountered. However, in

\startmode[foo]
...
\stopmode\enablemode[foo]

the contents of the mode environment are not execited because foo is not enabled when \startmode is encountered.

Checking for multiple modes (or/and statements for modes)

\startmode and \startnotmode can check for multiple modes,
by giving a list of modes as their arguments. \startmode
processes its contents (everything until the next
\stopmode, thus \startmode cannot be
nested.) if any of the modes are enabled, otherwise (i.e., when all
the modes are disabled) \startmode ignores its
contents. The opposite is \startnotmode: it processes its
contents (everything until the next \stopnotmode) if any of the
modes are disabled, otherwise—when all the modes are enabled—the contents are ignored.

\startmode and \startnotmode are "or" environments. They
process their contents if any of the modes satisfy the required condition. Their
"and" counterparts are also available: \startallmodes and \startnotallmodes
process their contents only if all the given modes satisfy the required
condition. For example, suppose you want to enable interaction (e.g., hyperlinks)
only when both screen and solution modes are enabled. Then you can
use:

To summarize, the four start-stop environments for checking modes are:

\startmode[mode1, mode2, ...]% Processed if any of the modes is enabled\stopmode\startnotmode[mode1, mode2, ...]% Processed if any of the modes is disabled\stopnotmode\startallmodes[mode1, mode2, ...]% Processed if all the modes are enabled\stopallmodes\startnotallmodes[mode1, mode2, ...]% Processed if all the modes are disabled\stopnotallmodes

These environments have \doif... alternatives that are useful for short
setups. Also, they can be nested.

\doifmode{mode1, mode2, ...}{Processed if any mode is enabled}\doifnotmode{mode1, mode2, ...}{Processed if any mode is disabled}\doifallmodes{mode1, mode2, ...}{Processed if all modes are enabled}\doifnotallmodes{mode1, mode2, ...}{Processed if all modes are disabled}

The logic for determining when the content is processed is exactly the same as
for the start-stop commands.

These \doif commands each have a variant to process alternative code if
the conditions are not satisfied (like the \else branch of \if).

\doifmodeelse{mode1, mode2, ...}{Processed if any mode is enabled}{else this is processed}\doifallmodeselse{mode1, mode2, ...}{Processed if all modes are enabled}{else this is processed}\doifnotallmodeselse{mode1, mode2, ...}{Processed if all modes are disabled}{else this is processed}

Note that there is no command \doifnotmodeelse because there is no need for it; \doifmodeelse may be used for the same effect (with the if and else branches switched).

Checking multiple modes in parallel (case statement for modes)

In addition to the above "or" and "and" environment which check modes is sequence, you can also check multiple modes in parallel. The syntax for such a "case" environment is as follows:

\startmodeset[mode1, mode2, ...]{Processed if either mode is enabled}[mode3, mode4, ...]{Processed if either mode is enabled}[default]{Processed if none of the above modes match}\stopmodeset

The same mode can be referenced multiple times, and all matching brances are executed.
The \startmodeset ... \stopmodeset environments can be nested. So, you can use

\startmodeset[mode1, mode2]{
Processed when either mode1 or mode2 is enabled
}[mode3]{\startmodeset[mode1]{Processed when mode1 and mode3 are enabled}[mode2]{Processed when mode2 and mode3 are enabled}[default]{Processed when mode3 is enabled and mode1 and mode2 are disabled}\stopmodeset}[default]{
Processed when mode1, mode2, and mode3 are disabled.:
}\stopmodeset

Checking modes in Lua

In MkIV, the state of any mode is accessible at the Lua end as tex.modes table. Specifically,

tex.modes["screen"]

returns true if mode screen is enabled and false otherwise. Thus, specific combinations of modes can be checked using boolean expressions. For example

if (tex.modes["mode1"] and tex.modes["mode2"]) then
...
end

checks if both mode1 and mode2 are enabled.

System modes

Besides allowing user-definable modes, ConTeXt provides some system
modes. These modes start with a * character. Here
only the more commonly used system modes are explained; see the ConTeXt modes manual
for a complete list.

Perhaps the most useful system modes are *mkii and *mkiv which
determine whether MKII or MKIV is being used. These modes are handy when you
want different setups for MKII and MKIV.

Other modes are useful for very specific situations. Some of these are described
below.

*first

Enabled during the first compile run

A document must be run multiple times to get the cross referencing,
table of contents, etc.
right. However, sometimes you need to do some external processing (e.g., graphic
conversion) that only needs to be done once. In such cases, the
*first mode is handy—it is active only on the first run of the
document.

*export

Enabled when \setupbackend[export=yes] is set

You may want to use different images for XML [Export]. The *export mode is useful in such cases.

*project

Enabled when inside \startproject ... \stopproject

*component

Enabled when inside \startcomponent...\stopcomponent

*environment

Enabled when inside \startenvironment ... \stopenvironment

*text

Enabled when inside \starttext ... \stoptext.

You can use the project-product-component structure for managing large projects
like a book series. See Project structure
for details of this approach. A product or its components may be compiled
separately, and you may want to do something different when a product is
compiled or when a component is compiled. To do so, you need to check for
modes *project, *product, *component, and
*environment; these modes are set when the corresponding structure file
is processed. For example, the *product mode is set whenever a
product file is read; more specifically, when \startproduct is
encountered. Similarly, a mode *text is enabled when
\starttext is encountered, and likewise for the others.

*frontpart

Enabled when inside \startfrontmatter ... \stopfrontmatter

*bodypart

Enabled when inside \startbodymatter ... \stopbodymatter

*backpart

Enabled when inside \startbackmatter ... \stopbackmatter

A large document is typically broken down into different section blocks:
frontmatter, bodymatter, appendices, and backmatter. Internally, these section
blocks are referred to as frontpart, bodypart, appendix, and
backpart. Each section block sets a system mode with the same name. So,
if you want macros that work differently in different section blocks, you can
check for modes *frontpart, *bodypart, and so on.

*list

Enabled inside a list entry

*marking

Enabled inside a marking

*register

Enabled inside a register

*chapter, *section, etc.

Enabled inside the corresponding section head.

Sometimes you want a macro to behave differently if it is part of a section head, a section number, a list, a marking, or a register. For section heads, you can check for modes *chapter, *section, *subsection, etc. Similarly, *list<code> is enabled inside a list, <code>*marking is enabled inside a marking, and *register is enabled inside a register.

*en-us, *nl, etc.

Enabled when the current \language is en-us, nl, etc.

**en-us, **nl, etc.

Enabled when the \mainlanguage is en-us, nl, etc.

ConTeXt provides support for multiple languages. Languages are recognized by
their IETF language tags, like en-us for US
English, en-gb
for British English, nl for Dutch, de for German, etc. A document
has a main language, set with the command \mainlanguage[...],
that is used for
translated labels like chapter and figure. You can also switch the
current language using \language[...] to change the hyphenation rules.
Whenever a language is chosen, its identifier is set as a mode. The mode for the main
language starts with two *. For example, when the main language
is US
English and the current language is Dutch, the modes **en-us and
*nl are set (notice the extra * in **en-us).

*figure

Enabled when a graphic is found

*interaction

Enabled when interaction is enabled

*grid

Enabled when grid typesetting is enabled

*pdf

Enabled when the main output is pdf

*dvi

Enabled when the main output is dvi

Other system modes: *figure is set when a graphic is found,
*interaction is set when interaction is enabled, *grid
is set when grid typesetting is enabled, and *pdf and *dvi
are set when the output is PDF or DVI. Others
are too esoteric to describe here. If you are interested, see the
modes manual mentioned earlier.

Specific Examples

Different fonts

Suppose you want to generate two versions of a document, one with times font and one with palatino. One way to do this is as follows: